فصلنامه مواد پیشرفته در مهندسی
سال سی و سوم شماره 3 (زمستان 1393)

In this research، Ti-6Al-4V alloy was brazed with 410 stainless steel by three different filler metals as silver-base، nickel-base، and titanium-base alloys. In order to obtain optimum clearance، brazing was done in three different clearances of 0. 02، 0. 04 and 0. 06 mm. Also، the strength and hardness of the brazing zone were investigated. The results of shear strength showed that the brazed samples with titanium-base alloy at the clearance of 0. 02 mm had the maximum strength among the different samples which was 149. 5 MPa.

In this paper، the effect of Equal Channel Angular Pressing (ECAP) process on the structure and mechanical properties of AM30 magnesium alloy was studied. The results showed a considerable effect of ECAP process on creating an ultrafine grain size structure. Scanning Electron Microscope indicated that the grain size dropped from 20. 4 µm in the extruded form to 7. 2 µm in the first pass and 3. 9 µm in fourth pass. The fourth pass presented higher ductility and lower yield stress in comparison with the extruded case. This behavior can be explained based on higher rate of texture softening versus the effects of the grain refinement on strength. The hardness test on the samples cross-section showed an increase in hardness and a uniform strain distribution at higher ECAP passes.

The objective of this study was to synthesize glass ionomer–forsterite nanocomposite and study the effect of incorporating forsterite nanoparticles to the ceramic part of glass ionomer cement in order to improve mechanical properties and bioactivity. So، Forsterite nanoparticles were made by the sol-gel process using different weight percentages added to the ceramic part of commercial GIC (Fuji II GC). X-ray diffraction (XRD) was used in order to characterize and determine grain size of the produced forsterite nanopowder. In order to study the mechanical properties of the produced glass ionomer cement-forsterite nanocomposite، the compressive strength (CS)، three-point flexural strength (FS) and diametral tensile strength (DTS) of specimens were measured. Statistical analysis was done by one Way ANOVA and differences were considered significant if P‹0. 05. The morphology of fracture surface of specimens was studied using scanning electron microscopy (SEM) technique. Bioactivity of specimens was investigated by Fourier transitioned-infrared spectroscopy (FTIR)، scanning electron microscopy (SEM)، and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The results of XRD analysis confirmed the nanocrystalline and pure forsterite synthesis. According to the mechanical properties measurements، the optimum weight percentages of forsterite nanoparticles for enhancement of CS، FS، and DTS were obtained equal to 3، 1 and 1 wt. %، respectively. Statistical analysis showed that the differences between all the groups were significant (P<0. 05). SEM images and results of the ICP-OES and FTIR tests confirmed the bioactivity of the nanocomposite. Glass ionomer-forsterite nanocomposite containing 1 to 3 wt. %-forsterite nanoparticles can be a suitable candidate for dentistry and orthopedic applications due to the improvement of mechanical properties and bioactivity.

In this study، the chemical composition، thickness and tribocorrosion behavior of oxide films prepared on Ti-6Al-4V alloy by anodising treatment in H2SO4/H3PO4 electrolyte at the potentials higher than the dielectric breakdown voltage were evaluated. The thickness measurement of the oxide layers showed a linear increase of thickness by increasing the anodizing voltage. The EDS analysis of oxide films demonstrated precipitation of sulfur and phosphor elements from electrolyte into the oxide layer. Tribocorrosion results indicated that the tribocorrosion behavior of samples was significantly improved by anodising process. Furthermore، the tribocorrosin performance of thesamples anodised at higher voltages was enhanced. SEM and EDS of worn surfaces indicated that the oxide layer on the samples anodised at lower voltages was totally removed، but for the samples anodised at higher voltages، the oxide layer was only locally removed within the wear track. Moreover، measurement of wear volume of the treated samples exhibited lower values on the samples anodised at higher voltages.

Silicon nitride has attracted a considerable attention because of its excellent properties such as high-temperature strength، good oxidation resistance، high corrosion resistance، good thermal shock resistance، high creep resistance and good thermal and chemical stability. There are several different fabrication methods for synthesizing Si3N4 particles. Such methods are mostly costly and kinetically slow and require lengthy heat treatment. In this study، Si3N4 compounds were synthesized by means of mechanical milling. In the mechanical milling route،Si powder (≤99. 0%) was milled under nitrogen gas for 25 h and heated at various temperatures 1100-1200-1300 and 1400 C for 1 h at the nitrogen atmosphere at a rate of 200 ml/min. Silicon powder was also annealed under a similar condition in order to evaluate the impact of milling process on the low temperature synthesizing of Si3N4. Phase identification and microstructural characteristics of products were evaluated by X-ray diffraction، scanning electron microscopy and energy dispersive spectroscopy. The Fourier transform infrared spectroscopy and thermal analysis were used for characterization of the formed bands and thermal treatment of the sample، respectively. The obtained results exhibited that Si3N4 powder was fully formed with two kinds of morphologies including globular particles and wire with a width of 100–300 nm and length of several microns at sintering temperature of 1300 C. This was confirmed by the Si–N absorption bonds in the FTIR trace. Based on XRD results، 25 h milling reduced temperature of reaction remarkably in comparison with direct nitridation of Si powders for 1 h. With an increase in the reaction temperature، the Si3N4 samples had a phase transformation α→β، and variation of the morphology followed the vapor–liquid -solid mechanism.

Today، along with the advances in circuit printing technology it has become possible to fabricate band lines integrated with circuit elements. The band lines are known as microstrip lines and the whole packages are called microstrip antennas. The microstrip antennas have three layers، including conductive patch layer، dielectric sub layer، and ground conductive layer. One of the most important problems of prevalent antennas is their inflexibility، which was addressed in the current paper using textile based structure with proper flexibility and flexural stiffness. This was done using ink jet printing techniques followed by electrolytic plating to provide diverse antenna patterns based on nickel particles. The coated surface was characterized by scanning electron microscope، elemental analysis and optical microscope. Moreover، the washing fastness and the other physical and mechanical specifications were measured using standard techniques. The elemental analysis of metal-coated fabric clearly indicated a high level of nickel. Furthermore، the morphological investigation proved the formation of homogenous nickel nanoparticle in a diameter range of 100-500 nm with an evident boundary and semi-spherical shape. In addition، the cumulative presence of particles in a sequence followed a cabbage-like structure originating from metallic crystals. The washing fastness tests revealed a high stability in electrical resistance after several washing steps. In the meantime، the antenna gain and the corresponding bandwidth were measured using spectrum analyzer. The results indicated a 1 kHz increase in bandwidth and 11 dB decrease in antenna gain for a large size compared to a small one. Meanwhile، the bandwidth of rectangular pattern showed a 0. 2 kHz increase and 2. 5 kHz decrease compared to spiral pattern. Finally، the four-probe electrical conductivity test demonstrated a high level of conductivity around 2632 S/cm.

In this research، ZrC nano particles were synthesized by self-propagating high temperature (SHS) using the mixed powder of ZrO2-C-Mg and NaF or NaCl diluent. The effect of different proportions of raw materials، milling time، composition of the diluent and also pickling on the synthesis of ZrC was investigated. Optimal amounts of magnesium and sodium fluoride for the synthesis of ZrC were 2. 8 and 2 mol، respectively. Milling process of 120 minutes decreased the diffusion gap of raw material and increased the combustion reaction progress. XRD and SEM analysis showed that the NaF diluent more than NaCl caused a reduction in the size of the particles of ZrC and increased the progress of the combustion reaction. Synthesized samples were subjected to pickling in order to remove impurities of MgO by 37% HCl، and distilled water was used to wash off NaF and NaCl residues. ZrC particle size of different samples were in the range of 50-90 nm.

In this study، the effects of different parameters on charpy impact properties of pure and hybrid composite laminates reinforced with basalt and glass filaments were investigated. For this purpose، five types of basalt and glass laminates with quasi-isotropic stacking sequence، namely، a pure basalt، a pure glass، two inter-ply hybrid and one intra-ply hybrid composites were produced. Epoxy resin was used as matrix material. After that، the impact test was performed and the average absorbed energy of each type of specimens was determined. The results indicated that the pure basalt and nylon laminates had the highest and least absorbed energy، respectively. The hybrid laminates had the absorbed energy somewhere between the pure basalt and glass ones. Also، between the hybrid composites، the intra-ply laminate had a better impact performance than the inter-ply ones.

In this paper، the behavior of energy absorption of crush-boxes، made of Aluminum foam advanced material، was investigated based on foam cellular structure homogeneity. Therefore، thin-walled tubes of Cu-Zn30wt. %. brass alloy with 27 mm diameter and 1 mm thickness were filled with A356-10vol. %SiC-Xwt. %. of TiH2 foam liquid. Foam samples with 1، 1. 5، 2wt. %. of TiH2 were prepared by Form Grip into the brass tubes in order to produce crush-box. Then the crush-boxes as energy absorber elements were compressed by un-axial loading and then behaviors of progressive buckling foams were measured. Results showed by decreasing A356-10vol. % SiC foam density from 0. 93 to 0. 88 and then 0. 43 g/cm3، the energy absorption would be changed from 12955 to 13465 and then to 11192 J، respectively. The sample with 1. 5wt. % of TiH2 and density of 0. 88 g/cm3 had the maximum energy absorption. Also، the results of foams cellular structure images showed that foams of homogenous cellular structure had a sizeable effect on the progressive buckling behavior. We developed a new parameter as «sorting coefficient»، which can release the foams cellular structure non-homogeneity، and change the crush-boxes energy absorption during the progressive plastic buckling.

Nickel ferrite based cermets and their relevant composites have been widely used as inert anodes for aluminum electrolysis due to their good combination of chemical resistance، thermal stability and mechanical properties. In this study، various NiO/NiFe2O4 composites consisting of 5، 10 and 15% NiO in conjunction with Cu/NiFe2O4 cermets containing 0. 5، 10 and 15% Cu were prepared by powder metallurgy method. The degradation resistance of the developed inert composites was examined under hot corrosion condition by plunging samples in to the molten electrolyte at 1000ºC. The strength، toughness، hardness، relative density، microstructural observation، phase analysis and electrical resistivity were evaluated by 3-points bending tests، Vickers method، Archimedes method، scanning electron microscope، x-ray diffraction and conventional direct current four-probe techniques، respectively. The experimental results for NiO/NiFe2O4 composites showed that a significant improvement of toughness and degradation resistance continuously occurred with a moderate decrease in strength by increasing NiO content، while the relative density was increased only up to 5%NiO content. By increasing the Cu content in the cermet samples، all the properties such as strength، toughness and electrical conductivity were improved considerably but the degradation resistance decreased.